1. Field of the Invention
The present invention relates to the field of liquid crystal displaying techniques, and in particular to an LED backlight source and liquid crystal display device.
2. The Related Arts
As the technology continuously progresses, the development of backlight technology of liquid crystal display device also continuously grows. The conventional backlight technology of liquid crystal display device uses cold cathode fluorescent lamp (CCFL). But as CCFL backlight has the disadvantages of poor color recovery, low light-emitting efficiency, high discharge voltage, poor discharge characteristics at low temperature, long time to reach stable grayscale, and so on, the backlight technology employing LED has been developed.
In liquid crystal display device, the LED backlight source and the liquid crystal display panel are disposed oppositely face-to-face so that the LED backlight source provides light source to the liquid crystal display panel, wherein the LED backlight source comprises a plurality of LED strings, with each LED string comprising a plurality of LEDs strung in series. To drive each LED string, a dedicated driving circuit must be used to supply driving voltage to the LED string.
FIG. 1 is a schematic view showing an LED backlight source of a known technology used in liquid crystal display devices. As shown in FIG. 1, the backlight driver includes a boost converter 110, a plurality of LED strings 120 connected in parallel and a plurality of backlight driving IC 130.
The boost converter 110 is to boost the input DC voltage to satisfy the requirements of the LED strings. The backlight driving IC 130 controls the connection/disconnection of the boost converter 110 and determines whether to shut down the LED strings other than any specific LED string based on the voltage over a resistor R1 of the specific LED string (i.e., the voltage at the negative terminals of a plurality of series LEDs of the specific LED).
When any LED string is shut down, the current of the LED string is zero and the voltage at the negative terminal of the LEDs of the LED string becomes zero. When the backlight driving IC 130 detects the voltages at the negative terminals of the LEDs of any LED string are zero, the backlight driving IC 130 will control to shut down all the LED strings other than the specific LED string so that the plurality of LED strings 120 is all shut down and turned off, which leads to the LED backlight source unable to supply display light source to the liquid crystal display panel and affecting the liquid crystal displaying quality.